Television tube grid structure



Nov; 19, 1957 R. zAPHlRoPoULos 2,813,772

TELEVISION "TUBE GRID STRUCTURE Filed Aug. 24. 195s INVENTOIL PENN ZAP/Ronan 0s FIG.

@GENT United States Patent TELEVISION TUBE GRID STRUCTURE Renn Zaphiropoulos, Oakland, Calif., assignor to Chromatic Television Laboratories, Inc., New York, N. Y., a corporation of California Application August 24, 1953, Serial No. 376,052

4 Claims. (Cl. S16- 19) The present invention relates to cathrode-ray tubes designed especially, but not exclusively, for the reproduction of images in substantially natural color. More particularly, the invention relates to a cathrode-ray tube of the type having a grid structure of parallel wires positioned adjacent to a striped phosphor coated screen, or

target electrode, and to a method and means for fabricat- .Okolicsanyi United States Reissue Patent No. 23,672.

The Okolicsanyi disclosure also makes use of such a grid as a component of an electron lens system to focus A the beam electrons into a pattern of thin parallel lines registered with the phosphor strips of the screen. This concept of PDF (post-deection-focusing) has been amplified and extended by Ernest O. Lawrence, and certain characteristics of the resulting structure have been described in the literature (for example, TeleTech Magazine for November 1951, page 38 et seq.). These as well as other features have also been disclosed in a copending United States patent to E. O. Lawrence, No. 2,692,532, dated 26 October 1954.

`In order to facilitate an understanding of the principle of the present invention, a brief description of one form of single-gun PDF tube will now be given. This description should be construed as exemplary rather than limiting, since it will be seen that the invention is obvi- `ously applicable to tubes constructed along different lines, such as tubes having a plurality of electron guns. In general, however, the tube to be described may incorporate a screen, or target electrode, made up of a relatively large number of very narrow phosphor strips arranged in a selected or predetermined chromatic sequence, such that when excited by an impacting cathoderay light is produced in the component colors red,l green, blue,k green, red, green, and so on. The surface of the phosphor coatings faced away from the support base is then coated with a metallic layer, usually called an aluminized layer or the screen in some other manner provided with an electrically conductive electron permeable coating.

A grid assembly is located adjacent tothe aluminized or conductive coating of such phosphor screen. grid may be made up of parallel coplanar linear conductors or wires, and so related to the phosphor strips that, in an electron-optical sense, there is a wire aligned with each phosphor-coated strip adapted to produce red light. These wires, for convenience of reference will herein be called red and blue wires and the related strips called red and blue strips. The wires related to each of the red strips are connected to a joined together electrically.

The

common terminal, while the blue wires are similarly Between the plane of the wire grid assembly and the conductive coating on the phosphor screen, there may be established a difference of potential of such magnitude and polarity as to create a series of converging cylindrical lenses for the electrons of the scanning beam directed to the screen or target. The lens system so functions that the beam electrons are caused to focus to a fine line pattern on the phosphor screen with an applied potential difference effective between the conductive coating and the average grid voltage of about three times that effective between the electron source and the grid, this line structure having no necessary direct geometrical relationship to the path covered by the scanning beam in tracing the lines of the image raster. g

It will now be appreciated that, as the beam electrons travel from the electron gun to the target they may be focussed by the above-described lens structure into a series of lines parallel to the phosphor strips. If there is a zero potential difference between the redl and blue terminals of the wire grid, then these lines formed by the beam electrons may be caused to.lie within the boundaries ofthe green strips. -If the Wires associated with the red strips are made positive relative to the wires electron-optically related to the blue strips, the beam electrons will be deflected laterally, and the thin lines will now lie within the boundaries. of the red strips. Similarly, the electrons will strike the blue strips when the wires associated with such strips are relatively positive with respectto the red wires. Different component colors are thus displayed according -to the potential difference (if any) existing between the -two sections of the grid wire assembly.

It will also be appreciated that the parallelism and other spatial relationship of these grid Wires (both to oneanother and to the phosphor strips of the target) is extremely important insofar as color delity of image reproduction is concerned. Furthermore, even though this parallelism and spatial relationship be carefully established during construction of the grid wire assembly itself, such a condition is not necessarily maintained during manufacture of the cathode-ray tube in which the grid wire assembly is incorporated. This is primarily due to the fact that one of the presently essential steps in cathode-ray tube manufacture is that of bake-out, in which the cathode-ray tube is subjected to high temperatures for a controlled period of time. During this operation, it has been found that uneven expansion of various parts of the grid wirev assembly (with subsequent contraction upon cooling) results in a loosening or sagging of the grid wires. Such a condition cannot be tolerated in. tubes which are expected to provide image reproduction substantially free from color co-ntamina-tion and excessive defocussing.

4One solution to the above problem which has proven to be successful in practice is set forth in a copending United States patent application of Howard R. Patterson, Serial No. 331,200, tiled January 14, 1953, and assigned to the same assignee as the present application. In the P-atterson disclosure, the relationship of the coeflicients of linear expansion of the grid wires and the grid wire support is so established that, with a rise in temperature, the wires of the grid will expand more than they support. Consequently, the grid wires will not snap with an expansion of the support member on heating of the assembly during tube bake-out, and, upon subsequent cooling of the tube, contraction of the grid wires will c-ause the latter to tighten so that a desired tautness of the Wires is obtained. Accordingly, by following the teaching of the Patterson disclosure, it is possible to manufacture cathode-ray tubes of the typel described in which sag, malpositioning, and excessive vibration of the grid wires is almost completely absent.

Ypart of the present invention,

However, it will be clear that, in employing such a process, a tight winding of the grid is necessary before bake-out, since no matter how great a variation may lexist between the coefficient of expansion of the grid `subsequent retention of the tautness originally present. Y It would accordingly be desirable to provide a manufacturing procedure in which an extremely tight winding of the grid wires before tube bake-out would not be necessary, and in which additional tautness if required,

couldbe added tothe wires in the course of the bakingout process itself. This would not only facilitate construction of the grid wire assembly, but would in addition provide even vgreater protection against the possibility of wire sagging or malpositioning than does the method ypreviously set forth by Patterson.

` One object of the present invention, therefore, is to provide Van improved form of cathode-ray tube designed especially, but not exclusively, for the reproduction of images in color.

, -A further object of the present invention is to provide, "in-ay polychrome cathode-ray tube having a grid structure of parallel wires, a method and means for fabricating this grid structure so that the wires thereof will be under substantially uniform tension and will retain their parallelism following bake-out of the tube into which the grid structure is incorporated. v

A still further object of the present invention is to provide a method and means for constructing a grid wire assembly, adapted for incorporation in an image-reproducing cathode-ray tube, so that the tension of any particular wire of the grid assembly may be greater following tube bake-out than it was before such operation was begun.

Other objects and advantages of the invention will be apparent from the following description lof a preferred embodiment and by reference to the accompanying drawings, in which: Figure 1 is a partly schematic representation of one form of cathode-ray tube in which the present invention may be incorporated;

Figure 2 is an enlarged view of a portion of Figure 1; .and

Figure 3 is a perspective view of a portion of the wire grid assembly of Figure 1.

Referring now to Figure l of the drawings, there is generally indicated by the reference numeral one type of cathode-ray tube in which the present invention may be incorporated. This tube 10 includes the usual components,

frequently called an electron gun,. for developing a beam of electrons, and suitable means for deecting this electron beam 12 in substantially mutually perpendicular directions so as to trace a raster image on the tube target electrode. Since these basic operational features are well known in the television art, no detailed description is believed necessary, although reference is made to the aforementioned Lawrence United States Patent No. 2,692,532 for a more extended explanation.

The target electrode of tube 10, for ease of illustration, i-s disclosedas forming part of a separate unit or assembly 14 mounted in any suitable manner adjacent to the transparent end wall 16 of the tube. Obviously, however, the end wall 16 when suitably configured may itself comprise `the target electrode if convenient or desirable. For certain construction details of the assembly 14, reference is made to this applicants United States Patent No. 2,683,-

.833, dated July 13, 1954, and application Serial No. 307,436, filed September 2, 1952. However, inasmuch as these constructional details do not constitute a claimed the description which follows, and it will merelybe stated that the assembly 14 (which includes a transparent base plate 18, a phosphor coating 20 thereon, and a grid of parallel conductors 22 adjacent to the phosphor coating 20) is positioned and supported within tube 10 so that the light produced by impingement of the scanning beam 12 on the phosphor coating 20 may be viewed by an observer through the transparent end wall 16 of the cathode-ray tube.

The base plate 18 may be of glass or other suitable material. The phosphor coating 20 is preferably in the form of a plurality of narrow strips which have the property of lluorescing in different component colors of the image to be reconstituted, these colors, for example, being red, green and blue. These strips are laid down side-by-side in a predetermined chromatic sequence. As best shown in Figure 3, the order chosen for illustration is such that they produce light in red, green, blue, green, red, green, and so on as scanned in sequence. This order, however, forms no part of the present invention, reference again being made to Lawrence United States Patent No. 2,692,532 for further details. The phosphor coating 20 is then aluminized or otherwise provided with a thin film of electrically-conductive electron permeable material on theside toward the source of the impinging electrons.

` The grid adjacent to the target surface 20 is composed of a plurality of parallelly arranged linear conductors, such as the wires 22, aligned with the phosphor strips.

A small section of the striped phosphor surface 20 of the they will be omitted from target electrode is illustrated in Figure 3 (which is not drawn to scale) in order to permit a clear showing of the phosphor strip sequence, it being appreciated that the illustration is for this purpose only.

There is a grid wire associated with each so-called red and blue phosphor strip, but none with the green strips. By cyclically varying the voltage of the red wires with respect to the voltage of the blue wires, different chromatic aspects of an image are successively presented. In this connection, it must be kept in mind that the drawings of the present application are not` to scale, and that the relative dimensions and spacings of the illustrated components are intentially distorted for ease of presentation and to aid in an understanding of the invention. In general, though, each pair of wires may, in an electron-optical sense, be considered as subtending strip areas including phosphors to produce all colors.

In a preferred form of the tube design, a potential is applied to the conductive coating on the phosphor surface 20 which is relatively positive with respect to the average, or D.C., potential of the wires 22 of the grid assembly. This gives rise to a plurality of cylindrical electrostatic lenses, which serve to focus the electrons of the scanning beam 12 into a series of fine lines registered with the phosphor strips. Thus, in effect, the wires 22 act as one component of a lens-grid. However, the present invention is obviously applicable to cases where the wires 22 serve as a color-changing device alone, as will subsequently appear.

Although any suitable method may be employed for positioning the wires 22 so that they are adjacent to the phosphor-coated surface 20 of the target electrode, a pair of bars 24 and 26 is shown, each of these bars having on its upper surface a series of grooves for aligning the -wires 22 and preventing lateral movement thereof at such structing the grid wire assembly of Figures l, 2 and 3 so that the tension of each of the wires 22 may be changed by the bake-out operation which takes place during manufacture of the cathode-ray tube. This is accomplished by utilizing for the grid assembly wire which has been cold drawn or has otherwise experienced hardening through an elongation, or other deformation, of its crystalline structure without subsequent heating. One example of such a wire is that known as #302 stainless steel hard drawn. When a grid unit incorporating such wire is subjected to the tube bake-out process, the high temperatures which are encountered (750 F. is normally reached) at least partially relieve the stresses in the wire. If the tension of any particular wire strand (resulting from stress relief occasioned by baking-out the cathode-ray tube) is below the yield point of the wire strand at the baking temperature, the wire strand will shrink because of the stress relief. The amount of shrinkage will depend upon the extent to which its original crystalline structure was deformed when it was cold drawn, upon the maximum temperature reached during the bake-out, and upon the time at such temperature. Shrinkage action of this `nature will usually take place in actual construction of cathode-ray tubes incorporating a grid assembly of the type under discussion.

If the tension of any particular wire strand resulting from stress relief is above the yield point of the wire strand at the bake-out temperature, the wire will not shrink, but, on the contrary, it will extend and permanently deform to the degree necessary to make the nal tension in the wire equal a value determined by the yield point of the wire at that temperature. However, since one of the objects of the present invention is to permit a relatively loose winding of the grid wire assembly, the latter of the two conditions set forth above should not be frequently encountered.

It will be noted that any shrinkage which may take place in a particular wire strand depends on (l) the original tension of the wire strand before tube bake-out, (2) the maximum temperature reached during such operation, and (3) the time at such temperature. Hence, by subjecting the cathode-ray tube to the bake-out temperature of approximately 750 F., a partial compensation is achieved for unequal tension in the respective wire strands following the winding of the grid assembly, as shown in the following table:

Change in tension before and after bake-out of four grid wires selected at random With a higher temperature, greater stress relief will occur, and a more complete compensation will be obtained.

lt has been customary to employ for winding grid structures of the type under discussion wire which had been annealed during each step of its manufacture. In such cases there are no stresses present in the wire which can be relieved by subjecting the wire to high temperatures, and hence there is no possibility of wire shrinkage or extension due to this factor alone. In effect, therefore, the use of cold drawn wire in accordance with the present invention causes the tube bake-out to constitute a stress relief process insofar as the wire is concerned, except that any resulting wire shrinkage, which previously took place during manufacture of the wire itself and which was of no benefit insofar as obtaining a tight cathode-ray tube grid assembly is concerned) now occurs after the grid is formed and adds a benecial tautness to each grid wire strand.

The amount of stress relief which occurs for each particular type of cold drawn wire under the temperatures to be encountered during tube bake-out depends upon its previous treatment, and will determine the final` tension of the grid wires, subject to the differential coeilicient of thermal expansion of the wire 22, the base plate 18, and the metal frame (not shown) of which the two retaining assemblies 28 and 30 of Figure l form a part. By properly selecting the respective coeicients of expansion of these elements as taught by the above mentioned Patterson patent application Serial No. 331,200, a desirable final tautness of the grid wires may be achieved.

inasmuch as the concept herein described utilizes the principle of stress relief, it is intended to embrace all types of wire'and all other iilamentary electrical conductors in which this characteristic is present to a preferred degree. Whether or not a particularjwire composition will exhibit the desired properties can in part be determined `from a consideration of the temperature range within which stress relief will occur for that specific type of wire. A few examples of Wire materials are set forth in the following table along with a suggested recovery temperature limit for each type, the period during which the temperature is maintained being chosen so as notto exceed a commercially acceptable maximum:

Suggested Recovery Temperature limit, F.

Wire Material 0l S .A." Nickel D Nickel (Magno) Advance (50Cu-50Ni) Super Nickel (30Ni-700u) Monel 430 Stainless. 446 Stainless 18-8 Stainless Hastelloy A Tungsten Molybdenum Copper- Silver Gold- Nichrome V Carbon Steel (Piano Wire) The recovery temperature limit set forth above is a function of previous treatment of the metal, of composition, of the method of producing the stress, and of the time at the selected relief temperature. Beyond this limit recrystallization occurs.

Having thus described the invention, what is claimed is:

l. The method of fabricating a grid assembly for a cathode-ray tube which includes the steps of arranging uncoated cold drawn wire upon a support so as to form a plurality of substantially parallel strands lying approximately in a single plane, with each such strand being supported at or near the extremities thereof, inserting the said supported wire into a cathode-ray tube envelope, and then baking-out said cathode-ray tube at a temperature less than that at which recrystallization of the wire occurs to at least partially relieve the stress in said wire caused by the cold drawing thereof.

2. The method of fabricating a grid structure for a cathode-ray tube which includes the steps of winding upon a support a continuous uncoated cold drawn wire to form a plurality of closely spaced substantially parallel turns separated from one another by a distance approximately that of one elemental area of the image to be reconstituted upon the target area of the cathode-ray tube with which the grid is to be assembled, each turn of said supported wire having a certain degree of tautness, inserting said supported wire within a cathode-ray tube envelope, and then subjecting said cathode-ray tube to a temperature lying within the bake-out range for said cathode-ray tube and which is less than that at which recrystallization occurs to change the degree of tautness of each turn of said supported and uncoated wire by at least partially reliev- `ing thestresspresent in said'wire caused by the lcold drawfinsfthersff f 3. hejmethod .of fabricating a grid structure for a 'the stressed state to the supports, positioning the supports and'thelthereon strung conductors within the cathode-ray ytube envelopefor tube evacuation, heating the assembly Ato a temperature which is sufficiently high for tube bakeout and within the stress relief range, below recrystallization temperature, of the uncoated conductors thereby to .relieve molecular stress within the conductors and removing theheat to increase the tautness of the conductors .with cooling.

4. The method of fabricating a grid structure for a cathode-ray tube comprising the steps of Stringing cold `drawn uncoated linear conductors in substantial parallelism and in coplanar fashion between supports separated from each other by a distance sufficiently great that the strung conductors span one dimension of a raster area to be traced, stressing the conductors to a tautness approachitgbt less lthan an optimum value, anchoring the conductors inthe stress state to the supports, positioning 4the ysupports and the thereon strung conductors within the cathode-ray tube envelope inthe region of the viewing window for' tube evacuation, heating the assembly to a temperature which is suticiently high for tube bake-out during evacuation and within the stress relief range, below recrystallization temperature, of the strung uncoated conductors thereby to relieve molecular stress within the conductors and removing the heat to increase the tautness of the conductors with cooling.

References Cited in the tile of this patent x UNITED STATES PATENTS 1,280,825 Paez Oct. 8, 1918 2,142,865 Zabel Jan. 3, 1939 2,463,535 Hecht Mar. 8, 1949 2,653,263 Lawrence Sept. 22, 1953 2,708,788 Cassman et al May 24, i955 FOREIGN PATENTS 689,564 Great Britain Apr. 1, 1953 

